Is there any legal way to go about either getting her to come get it or if I can get rid of it because of abandonment? Has she abandoned it?

This is not a landlord/tenant situation unless she paid you rent. If she paid rent, then you will need to follow Michigan law regarding abandonment which allows for removal under certain conditions. Since there was no agreement or lease, then you have the right to remove her possession. I would suggest that you advise her in writing that you will be disposing of all her personal property if not removed by a specific date. I would suggest that you repeat that she should have removed her personal property in January or February when she left or by the end of April as you advised. Unless this is a hardship for you, I would give 30 days for the removal. Remind her that you are going to charge for storage of her property. Good luck.

Have your notices been in writing, is there a garage where it can be conveniently be stored? I suggest you confer with an attorney with the details but it does.