My question involves landlord-tenant law in the State of: Indiana
I'm currently in a lease until the end of July with a girl I don't know very well. We've had a number of issues the past few months. To keep it simple and relevant, my roommate and I agreed on basic etiquette for the home (such as keeping our shared spaces clean, which hasn't happened... don't get me started) and to share the utilities. We had vaguely discussed the fact that I am rarely home (a max of three nights a week due to work and boyfriend) and therefore if utilities get high we would not be splitting them evenly, for fairness. However, every month we have been splitting them 50/50. The cable, water and sewage are in my name. The electric is in her name. We have nothing signed in writing.
My roommate had stopped paying me utilities in late December until a couple of days ago when she finally wrote me a check for January. But she hasn't written me a check for this month's utilities (it seems like she is waiting for me to pay her for this month first). Please note that I have never been late paying rent, utilities in my name or paying her for the electric bill. However, this month she is telling me that the electric bill is $110, when in the past it was no more than $60. It's Indiana and it gets cold here in the winter but I have only been home one night a week at MOST since the start of January, and I find the electric bill to be excessive for one person. Therefore, I am considering only paying her a small portion of the bill, as we discussed at the start of the lease.
A few weeks after moving in, my roommate posted a note on the fridge that neither of us signed but she called it our agreement, despite the fact that many of the terms I never agreed to and we never talked about. But I've left it on the fridge and it didn't cover the idea of not splitting the utilities 50/50, so I wonder if that fact, and the fact that we have a history of splitting them evenly, would work against me in court should she choose to sue for whatever I don't pay her in electric.
Given all the problems I've had with her not paying me (on time or at all), I am wondering what the legalities are behind me not paying her. She's a petty person and I feel like she'd jump at the opportunity to take me to small claims court or some such, but I'm not sure if she could or if she'd even have a case considering she's doing the same. What kind of risk am I looking at here if I decide to stop paying my share of the electric bill? Do you think her case would hold in court, should it come to that?
ETA: I am still technically living in the apartment since my things are still in there and I do stay there once a week or so. I've not had plans to do any subleasing. I'm not physically there often at all and rarely use any utilities but since I'm still living in the apartment, I wonder if this would hurt my defense.
ALSO: there is nothing in our lease about splitting utilities evenly or 50/50 or what have you. It only says they need to be paid in full by the tenant whose name is on them.

