I am a nurse in a large hospital. We are given non-specific PTO (paid time off). My boss has been calling people after they have called in sick questioning if they are truly sick. She is make people disclose details if they take "personal" time. Then, she is calling those people on a day they were not scheduled to work and telling them they need to come in because they are short-staffed. Can she legally call employees and check up on them if they are sick? Is it legal for her to ask about personal days? Can she make a person come in on their day off?
1) Can she call employees and check up on them if they are sick?
She can call whoever she wants to, but she is a fool if she starts asking personal information. Massive legal liability. If sick time is used, she can require a doctors note to return to work. If sick time has been exhausted, and the employee is not covered by FMLA (or equivalent law about granting leave in your country), the employee can be fired, but questions still cannot be asked. If the employee is covered by FMLA, questions still cannot be asked, but the doctor's note process is much more intensive.
2) Can she ask about personal days?
No, personal days are exactly that, personal. You are not required to say anything, and if she pushes at that, you can go to HR and she will probably be reamed.
Personal days may require approval before use, that depends on the guidelines your HR department has set forth. That approval should be purely schedule based. You might be asked for a short blurb for description, but you can literally just write "personal reasons".
3) Can she make a person come in on their day off?
The overwhelming odds are no. Even if the nature of your work is that you are on call, then you are on call, not enjoying a day off. There could be something in your contract that says you need to come in, but I highly doubt it.
Id take up all of these questions with your HR department, and get more information about what your specific HR guidelines are.
Unfortunately; this will probably get closed due to asking for legal advice (but a rephrasing of the question could bring it back on topic).
Anyway, going back to your questions (and ignoring the legal aspect of it):
Can she call employees and check up on them if they are sick?
She can do whatever she wants. Doesn't mean you have to answer the phone if she calls.
Can she ask about personal days?
She can do whatever she wants. You can always reply with "It's a sensitive personal matter; I'd rather not discuss it with co-workers". (repeat as necessary)
Can she make a person come in on their day off?
There's probably something in your employment contract that stipulates this; but if you don't pick up the phone, how's she going to make you come in?