I live in Pennsylvania and own a property with another person intended to be our primary residence. We agreed to split mortgage and utilities 50/50. Now she does not want to pay utilities because she is in a rental property somewhere else and only comes to this property 4 d/month. Does she still have the right to 50% ownership?

Of course she still has the right to 50/50 if she is splitting the mortgage with you 50/50. But is there a written agreement for the 50/50 mortgage split ?You can't dispute that arrangement as long as she keeps up her end of the bargain and pays on time. I can see why she doesn't want to pay utilities if she is not living there for a full month.

Whether she has 50% ownership or not depends on ONE thing only andf that's what the deed says. If the deed says she is a joint tenant or tenant in common, then she owns 50% of the property.

As to the agreement on the mortgage and utilities, do you have that in writing? Otherwsie, I doubt if you could enforce it.

You don't say whether there is any written agreement about anything except the mortgage. Whose name(s) are the utilities listed under? Oral agreements are worth the paper they are written on
What if you move out, nobody pays remaining utilities? What about maintenance costs?
Taxes? I think she shares equally in all the costs associated with the property she is half owner of. It is not a hotel where you pay when you use.