Re: Dissolution of joint tenancy
While it is true that joint tenants are presumptively equal owners, that presumption is rebuttable, and under the facts here, it would be fairly easy to rebut the presumption and show a court that you are entitled to more than half, probably more than 70%, of the net equity upon a sale partitioning the property.
If estate planning were a consideration, I might suggest severing the joint tenancy by deeding your interest as joint tenant to yourself, or your trust, as tenant in common. However, this step is probably not worthwhile for a younger person in good health.
One basic rule here is that, despite how legal title is held, equitable title tends to follow purchase money, i.e., the down payment, unless there is a contract between the co-buyers or evidence that a gift was intended. This is the principle of purchase-money resulting trust.
Also, upon partition, one co-owner can claim against the other for expenses reasonably incurred for mortgage, taxes, maintenance, etc., and often for improvements; however, a co-owner out of possession can counterclaim for third-party rents collected by the owner in possession (but not for "rent" from the co-owner himself, since each co-owner is entitled to possession of the entire property).
You don't say whether you are both liable on the mortgage, so I assume you are; I also assume there is no contract between you (written or oral) covering your joint finances.
A part of your strategy should be that any deal between you resolve all joint financial matters, and if that requires refinancing the property, I would make that a moderate priority, and any cost or detriment you incur (including nuisance value) to do a re-fi should further reduce her share, or if not, should be an incentive to cooperate.
One way to "improve communication" and get a realistic negotiation under way is to initiate a lawsuit for quiet title (to a 70% interest in you) and for partition, with reimbursement or contribution for your expenses. Your process server should be able to track her down, and after that, you and your attorney will have no trouble at all carrying on a meaningful dialogue with her attorney.
Your goal in filing a suit would not be to carry things through trial and court-supervised sale, but to bring her to the negotiating table.
