Patti Stanger, Widow Sues Over Lame Dates

'Millionaire Matchmaker' Patti Stanger ripped off a widow who was looking for love by hooking her up with a worthless dating service ... according to a new suit.

Heidi Williams claims she wanted to hire Patti to get back into the dating game -- her husband died a few years ago -- but Stanger said she was too old for her clientele.

According to the suit ... Patti referred Heidi to a friend's dating service -- Pretty People International. Heidi claims she dropped $15,000 for a PPI membership ... and Patti got a referral fee.

Heidi's lawyer says the service left her high and dry -- she only got one real date and one phone date.

Heidi wants a full refund times 3 -- $45,000.

We reached out to Patti's peeps and PPI ... so far, no word back.

For any curious single fellas out there ... here's a shot of Heidi.