If she's using her photo as her WhatsApp profile photo, you may be able to take that and do a reverse image search on it. I don't use WhatsApp myself, however if you can't just straight save the photo by right clicking on it or similar - take a screenshot of the open profile where her image is displayed. On a PC, you'd press the print screen button - on a tablet or phone you may need to look how to take a screenshot with your device but I know on both my Samsung phone and tablet, it's holding the power button and the home button down together for about 3 seconds.
Once you get your screenshot, you'll need to crop the image out, on a PC it's fairly simple - open MSPaint, press CTRL+V to paste, then take the rectangular selection tool, select the photo and press CTRL+C. Then either open a new instance of MSPaint or use the dropdown menu and select "New" - once you're sitting at a blank paint image press CTRL+V once again to paste the image into its own new image file then Save As - name your image and I would suggest saving it as a .jpg or .jpeg file type as any reverse image searches will use jpg/jpeg format with zero issue. On a phone it's a little more difficult as you'll need to find an appropriate app to do the same exact thing - crop her photo from the screenshot and save it as a separate image file.
Once you've gotten her image file cropped and ready, you can head over to www.tineye.com/ which is a very good reverse image search engine. You can also search under Google for "Reverse Image Search" and you'll get more sites that may give you a hit if Tineye doesn't produce any results.
For what it's worth, I don't actually condone snooping myself but I have worked with computers and in the IT field myself for my entire adult life so if you have any questions or if you need any further help - feel free to send me a private message and I'll try to help you out to the best of my abilities :) I'm sincerely sorry you're going through such a tough time right now. 