I agree with much of the 'stack' that rms80 suggested above--looks pretty similar to what I have used in the past.
Before recommending any supplements for your friend, however, I have a question. When you say that she is resuming marathon training, I presume that this means that she has run a marathon in the past. The only reason I ask is that I am incredibly hesitant to suggest endurance oriented supplements to someone who has not trained extensively at distance without supplementation. If one does not know how their body reacts to long distance training without added supplementation, it is difficult to diagnose any improvement or possible negative reactions caused by the added supplements.
This being said, I have found the following to be very useful:
--BCAA's pre and during
--WMS during and after
--Fish Oil (I usually go around 15-17g a day)
--Perhaps an added joint support supp (I like Animal Flex with Super Cissus RX added in when problems crop up)
--A cordyceps product to aid in CV endurance (I like Drive, but have heard good things about MST's line)
--Beta Alanine and Citrulline Malate (this stack is wicked for endurance)
Hope this helps--while these supps, save perhaps the fish oil and BCAA's, are hardly NECESSARY, they sure do help!