scans and concerns

Hi, I'll try to make this short and sweet but this a concern about scans.

Background: My mom was diagnosed with HER2+ in February 2008. It has metastasized and gone to her liver(almost completely loaded with tumors) and her ribs and I THINK her lower back(months before she had complained about a severe pain in her ribs. Mind you see has a very HIGH tolerance for pain....she broke her back in a horse riding accident and WALKED into the ER...just to give you an idea). Mom got an MRI and bone scan after the diagnosis, hence the above metastases. She's been on a weekly treament of Hercept and Navalbine adn a monthly IV dose of Zometa. She's had 2 CT scans about 3 months apart and monthly tumor counts. She's gone from 1500 tumor count to 34.9. First CT scan showed MAJOR shrinkage of liver tumors.(another give away months before her diagnosis...she was at a party and the thought of wine made her ill. Mom's an occasional wine drinker so this was very weird. Must have been her liver telling her something. Now she has no problem with a glass or two of wine.).  She just went for ANOTHER CT scan and the doc said very SMALL change, but for the better. Now the Doc is unsure if the spots on the liver are small tumors or scar tissue(mom develops SEVERE scar tissue). Of course I was working and couldn't go to the doctor to ask questions. The radiologist also suggested mom get a bone or PET scan. The doc is pushing towards PET because the zometa coats the bone and won't give a proper reading. Now my final question....no mention of a brain scan. the Doc says its rare for BC cells to go to the brain and an MRI would only be necessary if mom had symptoms. She doesn't but I think there should be a scan before it gets to the pain point. I read more doctors suggest this and that chemo and Herceptin CAN'T go through the brain-blood barrier so it's like her brain is unprotected(most likely would need gamma radiation if she got brain tumors). Mom is still very depressed. Mind you, she's worked at a hospital for 40 years and 95% of her relatives died of cancer so she is basically thinking....anytime now....God willing if I'm still alive NEXT year, I live from scan to scan, etc. I think she should get a brain scan but I don't want to seem pushy to the doc nor do I want to depress mom anymore(i think i already did by suggesting it). Anyone have brain scans or suggest them as a baseline?