I'm a fan of more is better, but in your case I understand how you need to limit it! 60'x60 should be lots for her. She's probably not going to want to run and buck and jump fences and all that anyway! She's just happy it doesn't take so much energy to "BE" right now! And it's not like you're trying to give her enough paddock to graze on. Freedom of movement and she will definitely have that with a 60x60 field.
Thanks all, I think I'm going to try that and see how it goes. Just to get her outside will be good. This is temporary, around the end of September, that's when the vet said whatever it is down here that affects the horses seems to go away!