I agree. Work like that is warrantied for 60 or 90 days. Take it back to the shop and demonstrate for them what is happening.
My bet is that the bobbin tension is set too high. A lot of people are afraid of adjusting bobbin tension but it's really easy if you simply know what to do. Once bobbin tension is set correctly, you can adjust top tension. Again, my bet is that the service person set the bobbin tension for straight sewing and never bothered to test the machine for embroidery.
If you are past the warranty date on the service, try adjusting the bobbin and top tensions yourself. I'm not familiar with your machine, but there are a limited number of bobbin types. Yours might be one of these:
http://welcome.solutions.brother.com...hf_inov700eeuk
https://www.embroideryaffair.com/mac...-tension-blog/
http://www.superiorthreads.com/educa...on-is-adjusted
The Pacesetter manual may help too:
http://homeappliance.manualsonline.c...xl-721-5116286
Finally, is your wife absolutely sure she is threading both the bobbin and top correctly? Plus, check both bobbin case and throat area of the machine for burrs. Even a small burr will cause thread to break. It's easy to sand off a burr using jewelry type sandpaper (not regular sandpaper). Also, try using a different brand of embroidery thread. Some machines are particular about which thread is used.
Edit: Next time determine cost of service before leaving your machine! And specify that they need to call if they find anything that would cost more than what is quoted, again before they do the fix.