Built it. I get most components for my survival kits at Walmart. Only when Walmart doesn't have what I'm looking for, or what they have is of substandard quality do I go to Amazon, EBay, GoingGear, Rei, Cabelas, Bass Pro Shop, Dickie, or Academy. Looking online first helps to define what you are looking for. Then it's just a matter of comparing prices.
A pre-made first aid kit is a good idea. Getting a good simple one and supplementing it is usually cheaper than starting one from scratch. If you want to make your own, I go to a crafts store and buy small plastic craft bags in different sizes. Those I use to hold pills (smallest bags), bandages, triple antibiotic foils, Alcohol swab foils, iodine swab foils (medium bags), and put everything in a larger bag. Making your own first aid kit this way is more expensive, but makes sense if you are going to make more than one.
Building your survival kit also gives you the opportunity to personalize the kit, specially since it is a gift for someone special. You know her, her skills, preferences, how long her average hike lasts (if she would actually use it for hiking and not just to keep in the car), and where she usually goes. You need to take these issues into consideration when selecting size, weight, and components.
Now, do you know what you want to include in the kit, or would you like ideas on what to include?