You can bring legal action seeking recovery of your deposit, and if the landlord failed to comply with the rules and timing regarding return of deposit, you might be entitled to penalties as well. You could bring Small Claims action for the $7500. If you sought penalties, you'd have to file in Superior Court. If this is in SoCal, and you are serious about getting legal help, feel free to contact me.

Take her to small claims court. Contact me directly for assistance.

Attorney Nelson is correct in his response. I wonder, however, what your monthly rent was because I believe that a security deposit is limited to no more than twice the rent for an unfurnished dwelling and three times if it is furnished. If your deposit was $7500, you rent would have to be between $2,500 and $3,700 per month. The landlord must return within 21 days of your giving up full possession [which includeds the keys] all of the deposit except for sums that she provides reasons for withholding. If she fails to do so she waives her right to bring up the issues of damage, etc. If you are not married or otherwise related to the other tenant, each of you may be able to sue separately in Small Claims Court to avoid the $7,500 plus costs limitation. You seem to have a good chance to get at least some of your deposit back. It might be worthwhile to retain an attorney to write her a single demand letter before you sue. With review of the materials and speaking to you, that might take 1-2 hours; the hourly rate for attorneys does vary somewhat.