Yes, first you need to know what your goals, motivations, and intentions are for the offspring.
Second, you need to be very honest about the horse in front of you. What ARE her strengths, but more importantly what ARE her weakness, why are they weaknesses, and is it conceivable to breed them out. If you have no intent to breed them out, then you have no intent on improving the outcome, you therefore have no business doing it, imo. While your circumstances may be solid now, anything can happen down the road and so you must try and ensure the resultant foal will be what's sometimes referred to as a 'good citizen', as well as 'useful' for others.
Third, adding yet a third breed to the mix is generally a mistake, particularly when you've already got a crossbred of two types, and are now adding a third type to the mix. It'd be different if the mare was a cross of the same type of horse, but she's not. Therefore, your best genetic odds lay with breeding her to an Arabian or a Paint, not a Fresien.