Is it possible to just have a personal aid to help with a shower once a week?

My 95 year old mother-in-law lives with us. I've tried to find someone to help mom with her shower once a week. All of the agencies I've talked with say that there would be a minimum of 3 hrs. to pay for. It doesn't take 3 hours to help a 4' 8" woman take a shower, but, the agencies say that the aid could clean moms room or make her meals or give her meds etc. I do all of these things for her, however, I'm a senior citizen myself with arthritis in my upper back, hips and shoulders and I'm simply not able to do this for her anymore. Mom can get into the walk-in shower (which has a shower chair) and back to her walker with a little assistance. She can wash her upper body but needs help with her hair, legs, back and feet. We live in North Charlotte.