She's been ill for a long time and still isn't well enough to get up.
Literal
She [topic-は] long-time illness [by-で], still get-up-can [to the extent-ほど] well-become not.
~ほど here sets a threshold: 'not recovered to the degree that she can get up.' 起きられるほどよくなってない layers potential (起きられる, 'can get up'), degree (~ほど), and negative becoming (よくなっていない, 'hasn't gotten better'). まだ ('still') emphasizes the ongoing state. The contracted ~なってない is casual for ~なっていない.