There lies the likely defence strategy. If you deliberately set out to poison someone with say, Cyanide, there's no mistake in what you're doing. It would be very difficult to give cyanide to someone accidentally. However, it may be a fairly easy to accidentally feed someone food that contained botulism - also a deadly poison.
Deadly mushrooms don't have a label on them and are amongst hundreds of thousands of varieties of mushrooms.
Can it be established
a) she knew they were extremely poisonous and didn't accidentally mistake them for safe mushrooms?
b) she knew feeding them would result in serious illness or death?
I personally believe her suspect behaviour points to her knowing exactly what she was doing but suspect behaviour isn't proof. It's just a link in the chain of evidence...
MOO
The problem for her is that she has said she bought the mushrooms at the market. She will have to disavow her previous statement and admit she lied about where she got them. Also, she made that claim a good month after the deaths. This wasn't something said under questioning while panicking, but rather a signed statement that was put out by her attorneys.
It will be tough for her to walk that back and maintain any semblance of credibility.