Without any pre- and post-Invisalign photos of your teeth, it would be hard to make accurate diagnosis and recommendations.
However, in general, if your teeth were flared to begin with, and you wanted to "straighten" your teeth, this needs to be clearly defined. When lay people talk about "straightening" the teeth, it could mean anything from just align them by proclining, or tipping, the teeth in a straight line, to uprighting the teeth by retracting them.
Aligning the front teeth is simple. The question is whether you wanted the teeth to be retracted back ("pushed back in") or proclined ("pushed/tipped outwards") is the question. This is something that no orthodontist will be able to just do it because everyone's idea of straight teeth is different. Some orthodontists (including myself) will be very specific with the patient at the initial consultation what exactly the patient wants done: for his or her front teeth to be "pushed in or out". Of course, I will complete thorough clinical exam and study the study models and radiographic measurements. But unless the crowding is so severe that extraction is highly warranted, most of the time, if the crowding is mild (<4mm) or mild-to-moderate (4-6mm), I would discuss this with the patient and talk about the options of extraction vs. non-extraction.
A lot of other biological factors play in this decision as well. For example, sex, age and race of the patient play key role in what would ultimately look best in the long run.
So, back to your original question. Can Invisalign fix the flared out teeth originally treated with braces that started out being flared out? No. Not unless you change the treatment plan which probably would require extraction of four first bicuspids (most likely). If you choose non-extraction option again with Invisalign, then the most you would do is reshaping of your teeth again, and the teeth will stay in more or less similar position (ie. be flared).
I would highly recommend that you speak to at least two, three or four orthodontists before you start your treatment again. Good luck.