Medicine or disease? Please help

My mother has Stage 3 lung cancer (Non-small cell carcinoma). Tumor started griwing into spine (T1 and T2) over the summer and caused radiating shoulder pain. Oncologist prescribed steroid - Decadron - 4x a day. She immediately experienced short- term memory loss and he said to ignore it as it was relieving pain (I disagreed). After complaints he started to wean her off and she was down to two a day last week.

She suddenly experienced major anxiety and couldn't remember her pill schedule so she missed some and overtook others. Took her to ER for brain scan (CAT scan) which was negative. Was back to normal two days.

Oncologist was upset she ended up in ER and I pushed back (he NEVER returns calls within a week or less) and we butted heads until he stated he was suspending chemo unless she admitted herself to an ER that day with the end result being a nursing home run by the state (she has only Medicare) for 24 hour care so HE is not libel if she gets weak and falls.

Mom is high maintenance - not one relative will help out as she's burned all her bridges. She was staying with me and my family a few days. There was constant whimpering, whining etc. However, my boss let me take half days and, unbeknownst to Mom, i set up our outdoor cameras inside. We caught her getting up and down from chairs constantly and no whimpering etc. She also was caught dissing us for not letting her stay and sounded 100% "normal". 

She was okay when I dropped her off an hour away where she lives. She's in asenior complex with a cell phone, landline and two emergency pull cords. She stated she think she went into shock when the oncologist - who myself and several other asked her to find a new one fir a myriad of reasons - suddenly suspended treatment. Gave her her pill list for a week til I can get there, made myself a copy and set up her pill containers.

Today was a nightmare via phone. She calls a family friend in her confusion repeating she didn't take her pills and didn't know what to do next and they contact me. 

W have about a foot of snow coming tomorrow and I begged her to lay low until a week from now (company just went through takeover/layoff and I was one of few soared). I can't tell if the meds messed her up, it's a mental issue/dementia suddenly or she, once again, is playing me. It sounds cold but close to a dozen people who know her - spouse and teen child included - all gave the same assessment. I just don't want to be wrong especially when I'm the only relative left who will help but can't physically be there for week. Any help is appreciated.