Mother diagnosed squamous skin cancer. Spot 6 inches up from her inner elbow. Best treatment? Have chemo creams ever caused this type to spread and or become resistant? Surgery best option?

Surgery is best. Your mom should have surgical excision. . 6 inches up from the inner elbow is a good site for closure as the skin is usually loose there. Topical 5 FU and imiquimod can be unpredictable and are reserved for actinic keratosis and superficial basal cell carcinoma. Topical 5 FU and Imiquimod are not approved by the FDA for use on squamous cell carcinoma yet. Don't take unnecessary chances.
A chance to cut... ... is a chance to cure. Chemotherapy creams are best for the pre-invasive stuff that leads to squamous cell carcinoma; now the horse is out of the barn and surgery is probably your best option. They don't cause it to spread. Left untreated, these cancers cover the skin. It's grisly. I wish your mom a speedy recovery while there's still time.