Her caring, thoughtful guidance has proven ( or proved?) to be a valuable...?

This is in the wrong section. But since you asked it made me curious...

Prove has two past participles: proved and proven. Proved is the older form. Proven is a variant. The Middle English spellings of prove included preven, a form that died out in England but survived in Scotland, and the past participle proven, a form that probably rose by analogy with verbs like weave, woven and cleave, cloven. Proven was originally used in Scottish legal contexts, such as The jury ruled that the charges were not proven. In the 20th century, proven has made inroads into the territory once dominated by proved, so that now the two forms compete on equal footing as participles. However, when used as an adjective before a noun, proven is now the more common word: a proven talent.

with has- proven

without has proved is correct

guidance proved to ..

guidance has proven to...

It depends on the nuiance of the tense you want. There is little difference. The use of has makes it more of an enduring thing rather than a one time deal, meaning it was valuable multiple times.

It's proven.

If you take out the word "has" you would use proved. Ex:

Her caring, thoughtful guidance proved to be valuable

Her caring, thoughtful guidance has proven to be valuable

Your statement is past tense so I would go with proven.

Both are correct, but 'proven' is a more archaic form.

I'd say "proven".

Sounds right to me.

Who is "her"?