My comments pertain to an Easton Blues or Jazz aluminum arrow fletched with three, 5" feathers, cut 1/8" past center with a B50 type of bowstring.
http://www.eastonarchery.com/products/product/30 http://www.eastonarchery.com/products/product/32 If she would shoot her longbow with a full length (no cutting) 29", 1716 arrow with a 150 grain point weight, she will have a hair stiff tunable arrow. You can add or lower the point weight depending if the arrow is hitting stiff or weak at 20 yards. Total arrow weight will be around 452 grains, 15.06 GPP (grains per pound), 14.6% FOC, close to 147 fps in speed and have 21.5 foot pounds of energy. A very nice hunting arrow for her. BTW, don't be scared of the 15.06 GPP since I shoot, depending on which of my two bows I'm shooting, 14.86 to 15.16 GPP.
However, there is another way to tune a bow. You would have to adjust the brace height a little. When I tune my bows, I also adjust brace height. Using Stu's DSC program, for my 37# bow, I was almost spot on with a 2114 arrow tipped with a 185 grain point weight. But, the arrow was "showering" stiff at 20 yards since it was shooting to the left about 4". I lowered the brace height from the recommended 7.750" to 7.687" and shot the arrow with the 185 grain point weight. It was about 2" to the left at 20 yards. It was still showing stiff, but I thought it was a false positive. I had heard through the grapevine Blacktails like a stiff arrow. Going against conventional wisdom and instead of adding more point weight, I put on a 180 grain field point without lowering the brace height anymore. Dead on at 20 yards with the 180 grain point weight and later, also with a 180 grain broadhead. Which means my Blacktails "do" prefer a stiff arrow.
I achieved the lowering of the brace height by untwisting the bowstring by one half twist (180 degrees). You can do the same thing for her bow and arrow setup with just a little bit of experimentation.
You can get the 1716 Blues or Jazz shafts at Bowhunters Superstore and don't confuse this place with the rip off Bowhunters Supercenter. The Superstore is where I have been getting my aluminum shafts for the last 30 years. For experimentation, you can buy the Blues shafts by the half dozen (6 pack) and they cost ($19.99) while a half dozen (6 pack) of the Jazz shafts are ($20.75). The link is below.
http://www.bowhunterssuperstore.com/arrow-shafts-easton-c-520_593.html?page=3&sort=2a