I'm sorry to hear that you are having such difficulties with your former roommate.
The law in Ohio says that you have eight years to sue on breach of a written contract. Sed the Ohio law below.
So, you don't have to do anything now, you have eight years from the date that she breached the agreement, which was her refusal to pay her share of the rent to sue her.
However, since the room she occupied is padlocked, she may argue that you deprived her of her right to use the room. Therefore, I would suggest that you try to get another roommate in there as soon as possible to mitigate the risk that she will say that you caused her damage by depriving her the right to use the space that she will ultimately be responsible for paying for.
2305.06 Contract in writing.
Except as provided in sections 126.301 and 1302.98 of the Revised Code, an action upon a specialty or an agreement, contract, or promise in writing shall be brought within eight years after the cause of action accrued.
Amended by 129th General AssemblyFile No.135,SB 224, §1, eff. 9/28/2012.
Effective Date: 07-01-1993
Related Legislative Provision: See 129th General AssemblyFile No.135,SB 224, §4
See 129th General AssemblyFile No.135,SB 224, §3
Good luck to you. I wish you all the best.