Thank you. First of all, there are two separate claims here, in that one is for the rent and one is for the damage, so you could have two separate small claims cases. You'd have to have two to get over the $5,000 limit.
As far as representing your grandmother, the ONLY way you can do this is if you're a lawyer. That is, only an attorney at law is allowed to represent someone else in court. If your grandmother is incompetent, you can hire a lawyer on her behalf. If she's able to act, then she'd need to do this. But even someone who is an appointed guardian can't represent someone else in court, even a small claims court. Now you can assist her, help her with the paperwork, filing, etc... but she'd still have to be the one in court presenting the case to the judge.
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable.
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Thank you, ***** ***** luck to you!