Unfortunately, there are no porter services available before / during USCBP / U. S. Customs; they even prohibit cell phone use.
How heavy are the bags? Many airlines limit baggage to 23 kg / 50 lb, and may not at all slow baggage over 32 kg / 70 lb at all.
What she can do:
She'll arrive and process through immigration procedures first. As she proceeds into the baggage retrieval area, get a free cart or use a credit card to get a baggage cart, then proceed to the indicated carousel.
There, it's
possible there will be a representative who can help. These people, cleared to work in that area, are often there to intercept bags belonging to crew, etc.
Once the bags are on the cart, she pushes the cart to the Customs exit, turns her previously filled out U.S. Customs and Border Protection Declaration Form 6059B, and proceeds to the baggage check facility just outside US Customs. Personnel there will handle the bags.
I hope she has lots of time to connect; IAH can have long queues and chaotic processing, according to passengers. After processing lá side, she will have to make her way to the UA terminal and process TSA security.
Link to IAH website page with maps, etc.