Would Elizabeth (presumably??) have figured out how not to get married to Philip
Wrong Mary. It was Elizabeth's sister Mary who was married to Philipp of Spain. We're talking Mary Queen of Scots here who was married to a) Francis II of France, b) Henry, Lord Darnley (whom I guess you meant), c) James Hepburn Earl of Bothwell.
(Now Elizabeth's sister, Mary Tudor, had the same lessons Elizabeth had re: her father's marriages, but there really wasn't much of an alternative to marrying cousin Philip when she did. Her time of being able to give birth was running out due to her age, and Mary did hope for an heir of her body as opposed to having to pass the crown to Elizabeth. And her Habsburg cousins had been her champions ever since father Henry started to terrorize her mother because he wanted an annulment, plus of the unmarried European princes, Philip ones pretty much the best available by the time Mary became Queen. (Other than his father, whom young Mary was supposed to marry for a short while decades earlier. Now Charles V. marrying Mary in his old (for the time, he wasn't really for our days) age instead of making son Philip do so is another fascinating AU). Of course, Mary Tudor could have married one of her English subjects instead, but while this would have appeased the usual English xenophobia, it would have created anger and strive among all the nobles she didn't marry.)
But now back to Elizabeth and the other Mary:
What happens if Elizabeth and Mary swap when their personalities are in fact already set
Okay, in this case I think Elizabeth does avoid marrying Darnley, and she might even convert to get out of the situation of being a Catholic monarch in an increasingly hardcore Protestant state. However: she will still clash with John Knox (who in rl sort of mumbled a written "I didn't mean YOU" apology for the Monstrous Regiment of Women, but that was to Elizabeth, Queen of England, at a distance, whom he needed to be well disposed towars him, not to Elizabeth, Queen of Scotland, with whom he'd be struggling for power close up. And also, I'm not sure Elizabeth's method of using the marriage negotiatons game diplomatically, which gave her and England breathing space for years, would have worked with the much smaller and less powerful Scotland. The insistence that she'd marry and provide an heir among the Scottish lords would have been far, far stronger, and then she'd still have the same problem any Queen in that situation had: marry a subject and all the other nobles are pissed off, marry a foreign prince and everyone, nobles and commoners alike, hates that one as well. (Same goes for English nobles as suggested by the other Queen on the island.) Under the circumstances, Elizabeth might have gone for a continental Protestant prince regardless, though, one whom she could be sure would only spend a short time in Scotland, but those were thin on the ground. Eric of Sweden, who pursued her in rl, on paper would have looked good, but as he did go insane...
Meanwhile, Mary in Elizabeth's place with an already formed personality: marries Robert Dudley after the death of Amy Robsart, has the country in an uproar, gets deposed, I'm afraid. (Based on how Mary dealt with the Darnley fallout.) Unless she does marry her brother-in-law, Philip of Spain, immediately after her sister has died and before the Dudley situation arises, but I don't see her doing that.)
no subject
Wrong Mary. It was Elizabeth's sister Mary who was married to Philipp of Spain. We're talking Mary Queen of Scots here who was married to a) Francis II of France, b) Henry, Lord Darnley (whom I guess you meant), c) James Hepburn Earl of Bothwell.
(Now Elizabeth's sister, Mary Tudor, had the same lessons Elizabeth had re: her father's marriages, but there really wasn't much of an alternative to marrying cousin Philip when she did. Her time of being able to give birth was running out due to her age, and Mary did hope for an heir of her body as opposed to having to pass the crown to Elizabeth. And her Habsburg cousins had been her champions ever since father Henry started to terrorize her mother because he wanted an annulment, plus of the unmarried European princes, Philip ones pretty much the best available by the time Mary became Queen. (Other than his father, whom young Mary was supposed to marry for a short while decades earlier. Now Charles V. marrying Mary in his old (for the time, he wasn't really for our days) age instead of making son Philip do so is another fascinating AU). Of course, Mary Tudor could have married one of her English subjects instead, but while this would have appeased the usual English xenophobia, it would have created anger and strive among all the nobles she didn't marry.)
But now back to Elizabeth and the other Mary:
What happens if Elizabeth and Mary swap when their personalities are in fact already set
Okay, in this case I think Elizabeth does avoid marrying Darnley, and she might even convert to get out of the situation of being a Catholic monarch in an increasingly hardcore Protestant state. However: she will still clash with John Knox (who in rl sort of mumbled a written "I didn't mean YOU" apology for the Monstrous Regiment of Women, but that was to Elizabeth, Queen of England, at a distance, whom he needed to be well disposed towars him, not to Elizabeth, Queen of Scotland, with whom he'd be struggling for power close up. And also, I'm not sure Elizabeth's method of using the marriage negotiatons game diplomatically, which gave her and England breathing space for years, would have worked with the much smaller and less powerful Scotland. The insistence that she'd marry and provide an heir among the Scottish lords would have been far, far stronger, and then she'd still have the same problem any Queen in that situation had: marry a subject and all the other nobles are pissed off, marry a foreign prince and everyone, nobles and commoners alike, hates that one as well. (Same goes for English nobles as suggested by the other Queen on the island.) Under the circumstances, Elizabeth might have gone for a continental Protestant prince regardless, though, one whom she could be sure would only spend a short time in Scotland, but those were thin on the ground. Eric of Sweden, who pursued her in rl, on paper would have looked good, but as he did go insane...
Meanwhile, Mary in Elizabeth's place with an already formed personality: marries Robert Dudley after the death of Amy Robsart, has the country in an uproar, gets deposed, I'm afraid. (Based on how Mary dealt with the Darnley fallout.) Unless she does marry her brother-in-law, Philip of Spain, immediately after her sister has died and before the Dudley situation arises, but I don't see her doing that.)