It's hard to say as you don't know what her benefits will be in 2 years time when she needs to be able to sponsor you.
All of the rent excluding £20 because i live here will be paid by housing benefit.
HB has been frozen for 4 years from April 2016. If her rent goes up, any further shortage will have to be paid by her and reduce the spare money she needs to be able to sponsor you.
Full Council Tax
Is she still claiming single person 25% discount? Do they know you are living there?
Each council now decides who can have their CT reduced and who can't as they all now balance their own books. A change of policy within the council, or you moving to another area with a different council, could see this change in the future.
DLA (Higher Care Higher Mobility) £540 every 4 weeks
Unless she is in her 60s (whatever the age is) then at some point she will have to apply for PIP as DLA is being replaced by PIP. PIP has different requirements to meet for the levels of benefit amounts. Many who qualifed for the highest rate mobilty with DLA are not getting/saying they won't get thiis with PIP, as they can walk or use a wheelchair. Has she looked to see what points she will get with PIP?
ESA(Includes Disability & Severe Disability Premier) was £353 every 2 weeks
I'm not sure if PIP points being reduced from DLA, will have a knock-on affect with ESA or trigger another medical? Don't those on ESA have to have medicals every so often to see if their claim changes?
You might need to go a benefits forum about your plan to stop working as they will have a better idea about what benefit amounts might change over the next couple of years. Make sure that you tell them that you cannot have public funds.