I really feel for your mum, it can't be easy being in that situation. But if the proposed changes only increase the asset threshold by $50k, could she sell some of her artwork and furniture possibly? She could still get away with keeping her investment property that way..
And if she owned the property pre-sep 1985 then maybe she could sell it tax-free and use the money to buy a slightly cheaper property, so still earning a rental income.. And gifting some of the proceeds to you/your siblings (i know there's a gifting limit for the pension test to apply, but it may just be enough for her to not lose her entitlements).
Just trying to think outside the box
Look, at least she has assets to sell if she needs to. There are lots of people who are far worse off and still worked hard all their lives. Good on her for achieving what she has.