I have all of those as well as all of the citadel, game color and reaper masters so I'll just give you my two cents based on my own perspective on comparison between the ranges.
First impression would be to go for Game Color as they fill that niche with exactly what you described, brighter colors etc...however, the paint is unlike the model color range entirely and has a very inconsistent pigmentation across the line with no guarantee that one color will work out of the bottle the same as the next. I could go on but I'll just say simply, caveat emptor with those paints and if you must buy them stay away from the reds, yellows, greens and blues. The browns are ok if a bit satiny, the whites and blacks are fine and the turquoises and purples/pinks aren't bad. Oranges unknown, I don't use orange. *Actually the olive greens are good as well, I like those and again, all their browns except the yellow browns are good paints imho and the flesh tones are hit and miss. The dark to red skintones are fine and the light tones, but the dwarf flesh is bleh. Tan is a good one though. (I've literally gone through and rated each of their colors with a 5 star rating of my own for my notebook for quick reference, based on pigmentation, finish and overall quality. I've just done that recently so that info is still on my mind.)
So if your incliniation is to pick those up as a complement you might be dissappointed. Some painters work wonders with those paints though, I dislike them.
With Citadel paints, you're paying about two to three times the cost for paint that is decent, but why...you know, just why spend that money unless you're really fond of the line. Their foundation and washes are great, and sort of worth it, but only for the washes as the foundation paints are basically just Vallejo Model Color in terms of pigmentation and finish. I would just use a close match (there are plenty of conversion charts on the web) from VMC and be done with it, get twice as much paint for the cost. The washes though are terrific and imho sort of worth it since they're uniquely formulated and serve their purpose well. Not just as washes but tints and glazes and for other effects like weathering and mixing with pigments. They're quite handy. Other companies make washes in more colors with similar properties but I can't speak to those since I'm happy with the Citadel line.
Ok moving on. I would recommend Reaper Masters and High Def paints. She doesn't like mixing so she'll appreciate the "triad" system of paint they offer, shade, highlight and midtone. I disliked those paints at first because I was an early adopter, but they've long since greatly improved their formula and now they are very high quality paints which I don't hesitate to recommend. They come in droppers like your VMC's, so they complement there. They dry matte (used to dry satin) so they complement there, wide range of colors so again, a complement to the huge VMC line and finally they have all those bright colors she wants as well as super high quality clear paints and liners which are great to use for various tasks.
Running out of time this morning so I'll just finish with their newer HD line which was an answer to Citadel's Foundation line. Those are quickly becoming my new favorite paints because of their heavy pigmentation and flat finish, but again, if you already have the VMC line, then not really something you'll be astounded by as they behave similarly except they take less thinning. Game Color has a line of "Heavy" colors now called Extra Opaques but those are literally just rebranded Model Color. They are exactly the same formulation as the model color range so if you own them already, don't spend the money on them.
Just my opinion to help you before you spend money, your mileage as they say may vary. Buy a few of each and give them a go is your best bet even though you like buying complete sets, like I do. Gotta go, best of luck.
*Blah last thing: Regarding metallics, Vallejo Model Air and their line of alcohol based are the best you can buy followed by Citadel which have nice metallics but don't compare to VMA and especially their alcohol based metals which are just ...tops.
