By "gold machine" are you referring to gold jewelry or gold nugget prospecting? Just curious, because the Sovereigns, and I have owned several of them (4), are NOT what I would consider to be a gold nugget seeking detector. Therefore, no sense in getting the better half one like you have.
Now, while I have found gold jewelry with the Sovereigns, I found far more gold jewelry with the MXT. Probably 6 to 8 times as much!
The MXT is a good detector and might be the one to pick for her, but I have to tell you, the Matrix M6 really deserves a hard look. It has the same basic circuitry, same auto-tracking behavior, same discrimination range, and with the same sensitivity and discriminate settings they will operate virtually identically if the MXT is in the Coin & Jewelry mode.
Yes, the MXT offers the 'Relic' mode which is simply a dual-tone audio mode and the TID references are of typical relic hunting finds and not coin hunting finds. But for those who are mainly into coin hunting, the M6 offers the 7-Tone audio ID with the forward flip of the trigger toggle.
With either of them I would suggest a smaller-than-stock coil for most hunting because coins and other desireables are frequently located among various types of trash.
Both excellent picks, in my opinion.
Monte