She could get an event monitor that you don't wear and she would hold to her chest when she is having symptoms. It's wireless and has little metal feet that go against your skin.
http://www.amicardiac.com/patients/patient-instructions/heartrak-II-monitor
http://www.tzmedical.com/product.php?product_id=44
There are also ones that are sticky and stay on for 2 weeks. These just stick to your skin and once the come off, you just mail them in. They are also wireless. I personally have no experience with these but had a friend use one. He didn't have any events while wearing it but had no complaints about it.
http://www.ecouterre.com/stick-on-zio-patch-diagnoses-irregular-heartbeat-in-cardiac-patients/
http://medgadget.com/2011/05/lifetouch-stick-on-cardiac-monitor-from-isansys.html
So I just did a bunch of googling and found what your Dr is likely talking about!
http://www.medusoft.com.au/merlin.html
It is a post-event monitor that you wear as a watch and it requires no chest leads.
I've never heard of that watch. I currently have my 2nd 30 day monitor within the last couple of months and the easiest way for me to exercise is to put my recorder between my chest and sports bra. It holds it extremely well and doesn't pull on the cord or my arms don't get tangled in the cord. Doing something like that might help make playing tennis a little easier for her.
I'm familiar with several different types of ambulatory monitors but have never heard of watch type device one. There are watches that do check a HR but they just give you the pulse at that point in time (and often times not very accurately!) and don't record anything or look at the rhythm. Never heard of an event monitor like this though. Perhaps it is a new model and they are just being introduced?
I personally have not heard of a watch that records what is going on. I have a watch that tells me what my beat rate is but that is about it. I know there is some sort of heart monitor pen that came out but to get an accurate diagnosis it is really beneficial to catch the beginning of an episode and any hand held device would not capture that. I have had 2 types of monitors in my life a 24 holter monitor that was kind of big and bulky and annoying and then I had a 30 event monitor that was more like an ipod and had only 3 wires where I would actually record and episode when it started. The device was always recording a bit but only saved once I hit the button. In the whole scheme of things the most important thing is to get the episodes capture. So a few days to maybe a month of being inconvenienced may be worth it to know what is going on. Take care.