It depends on what the trust itself says about how the assets can be used for your mother's benefit, and on who the trustee is.
Typically, such trusts will specify that the assets can be used for the "health, maintenance, and support" of the beneficiary; sometimes for their "comfort, welfare, and happiness." You need to review the trust and see what the one controlling your situation says.
Caregiving costs should be covered under either one of the standards described. Still, not all trusts are so general. Some can be specific about what is, and is not, covered.
Another thing to be aware of: Who is the trustee? Is it your mother? Is it you? Is it another sibling?
Ideally, someone other than you is the trustee. That way, if you are paid a reasonable salary -- what a third-party would receive for the same work - wouldn't look like a conflict of interest.
If you are the trustee, be very careful to avoid anything that looks like such a conflict. As a first step, send out a notice to all the other beneficiaries, informing them that you intend to pay yourself a salary, and stating what it would be. Such a notice should give them time to object to such a move; if you learn of no complaints within that time period, go ahead and start with the payments.
Finally, you should check with the local probate court to see whether it enforces a standard time limit for such an action.