it would probably work, i'd use a q-tip or something to put it on though, and make sure she doesn't rub it into her eyes. the vinegar may make her eyes water, though. here's a good solution to use for tear stains.
Milk of Magnesia, corn starch and peroxide (20 volume to 40 volume)
Use equal volume of MOM and peroxide, and then use the corn starch to make a good paste of this; put on and work well into the stained area and let dry overnight. Wash out, CONDITION WELL. Keep doing this for several days until tear staining is gone, although I would recommend skipping a day or two between applications if possible. I also like to use a few drops of Nexus KerapHix in this mixture to help with conditioning.
This MOM formula is my personal preference when I do need to remove tearstain color from the face of my dogs. It works quite well overnight.
http://www.bhejei.com/tearsta.htmCounseling Clients:
Clients will naturally ask for advice regarding coat condition and general grooming problems, one of which is tear stains on white coated dogs. Suggest your customer provide bottled water only (preferably distilled) for his/her pet....seems mineral content in tap water may contribute to staining. Red dyes in some dog foods may also be a contributing factor. In addition to altering the dog's intake, it may be beneficial to use a tear stain preparation and/or to dab a little cornstarch on the 'tear path' in order to keep the area dry.