Stop and figure out whether you really need a conservatorship immediately. It's not always necessary. If you need to sell stock to finance her care, start by calling the broker
and finding out what information or documents he requires to complete the transaction. You may find that the brokerage firm will let you write a check on your parent's account without a legal conservatorship. It may only require a signed durable power of attorney for finance, or a multiple-party account. Depending on your relationship with the brokerage company, it may have other solutions that will allow the transactions to proceed. And you may be able to make all these things happen without a conservatorship.
If not, find an eldercare attorney in the county in which your mother resides. Explain the situation. A good attorney should be able to go into court ex parte, on an emergency basis, and establish a conservatorship, with you named as conservator, on an expedited basis. Expect this job to entail at least five to ten hours of attorney time. Remember, you don't need an attorney from a big (and probably expensive) firm to do this. Often the attorneys who handle such matters are sole practitioners, or are in smaller firms. In some areas paralegal services can help you complete this process yourself, which will likely be cheaper. Call your local county bar association for referrals.