We are having an 80th birthday party for my mother (2 sisters are
hosting/inviting).  My
aunt has given a substantial amount of money (non solicited) toward
the party.  How does one recognize her generous efforts?  Does she
need to be included with us as hosting the party or is an
aknowledgement appropriate.
Thank You

At first, I thought the two sisters were those of your mother, but I
guess they are her two daughters (you and your sister).
So the aunt is your mother's sister, and she cannot join you?
If so, I would suggest that you ask her to write a letter appropriate
to be read by one of you to your mother and the guests at the party
(in addition to whatever personal greetings she may address directly
to your mother).
Then you can take this as the opportunity to express your appreciation
for her generous support and your disappointment that she cannot be
there for the occasion.
Even without the letter from your aunt, you could do this.
She would probably appreciate a card with greetings and thanks signed
at the party by everyone there who knows her.  This would not only be
a nice gesture but would also confirm that her participation was
recognized.
I hope it is a grand occasion.

I need to clarify my question.  The 2 sisters are daughters of the
birthday party honoree.  The aunt is a sister-in-law to the honoree
and is invited and will be there.
My question comes to the point of wording in the invitation that will
be mailed to the invitees, does the sister-in-law need to be
recognized as giving the party (along with the 2 daughters) or can she
be mentioned at the bottom of the invitation with a special thank you.
 Please remember her contribution was not solicited by the 2 daughters
giving the party.
Thank you

The special thank you is what i would do.But instead of specially
thanking her i will leave a section at the bottom such as "Warmhearted
birthday wishes" with all the family member names but with this aunts
name on top.Or you could put a special
unique place that will be seen first as the invitation is opened with
"Best wishes" from this aunt.

Yes, thanks for the clarification.
It would seem only polite to assume that the aunt does want to
included as one of the hosts and give her the choice of saying that
she prefers not to be mentioned on the invitation.
You could show her the text for the invitations, maybe with an
alternate text, but both including her name with those of the sisters,
perhaps in the form:
"Mrs Xxx Yyy, Mary Aaa and Betty Bbb"  or  
"Our Aunt Xxx joins us in inviting...", or 
"Mary and Betty together with our/their Aunt Xxx"  or 
           "... together with their aunt, Mrs. Xxx Yyy"

If the aunt does not want to be on the invitation, let her say so.

Obviously, my suggestion of a letter from her is not appropriate, but
you could clarify with her whether she wanted to say a few words at
the occasion, or whether she would prefer that one (or both) of the
sisters mentioned her in her  words of welcome to the guests.  And if
she didn't want that either,  I would still mention her.

I hope this helps  - maybe to suggest to you something else.