Different uses - the DW 18 volt system has 2nd fix nailers (16 and 18ga) as well as a couple of staplers (well, certainly at least one), but you won't find a trade type gun which does both. The reason is relatively simple - staplers require a drive pin which is the width of the staple crown, pinners (2nd fix nailers) only need a very narrow driver. If you consider that a pinner has to be set up to sink the heads of the pins just below the surface attempting to do that with a 6 or 10 or 14mm drive pin, as you have with a stapler or combined stapler/pinner (there are cheap pneumatic combi guns around), would leave a large unsightly dent whenever you drove a pin.
Also different sizes for different uses: fencing - 1st fix nails (2.5 to 3.1mm diameter clout head nails); general cabinet / furniture making - probably 2nd fix 18 gauge combined with glue (16 gauge and 15 gauge are more for 2nd fix construction work such as fixing architraves and skirtings); upholstery - staples (narrow crown); hardwood trim to MDF shelving - 2nd fix pinner (18 gauge or 22/23 gauge). 22/23 gauge is what trade shops use as the pin holes are a lot smaller tha 18 gauge. Unfortunately that means you'd need 2 or possibly 3 different guns to cover everything because different size fixings need different size guns.
TBH if you want more bang for your buck you'd be better off doing something like buying a small compressor kit, such as
this one from
Machine Mart (there are others, but this one has a combined stapler/18 gauge pinner):
then adding decent quality pneumatic guns to it as required, than shelling out £500 to £700 on three DW cordless guns (bare). Note that DW make a very competent manual stapler which also fires 18 gauge pins.
The other thing to mention is that whilst cordless guns work perfectly well on site, they are big, heavy and unwieldy for bench use - trade shops generally use pneumatics as they are cheaper and lighter to use, not to mention being easier to positions accurately and extremely long lived (as a result of simplicity)
Also my daughter is considering starting a picture framing service as she is asked numerous times to make up pictures and frames
For picture framing your daughter probably needs to look at two completely different tools, a frame joiner like
this one:
which drive a V-nail or corrugated fastener into the underside of the mitre joint. There are manual versions of this which are cheaper, but a lot more hit and miss to use I found (costing £15 to £20 or so from art shops):
The other tool to consider is a sprig or point setter like
this one:
which drives triangular sprigs or points which hold the glass, matte, picture and backing board (apologies if the terminology isn't 100%, but I'm a "wood butcher" not a picture framer), etc in place. There are alternative systems to do the same job and Framers Corner do a similar DIY gun at about £30. The web sites of the two firms in the links (Framers Corner and Lion) are worth looking around to see what is used and available for picture framing, both tools and materials.