How is the sunlight exposure...geraniums are sun lovers.
Drainage....the soil should drain well..the geraniums, while they do take increased amounts of moisture, they don't like their soil to be forever wet...and soggy.
Roots, in that sense, would take no time at all to rot.

Where the soil IS soggy, eventually the roots become water logged...then they are unable to take up any further moisture--ergo, no further nutrition.

I will assume your question also refers to newly bought stock....not plants that have been left in the ground in a zone 5.

I suggest the soil for geraniums should consist of leaf mold, some peat moss, sand and lime mixed into a percentage of loam. (topsoil)

A feeding of fertilizer is given when new leaves form and generally a regular feeding program is kept up.....about every two weeks an application of liquid fertilizer.
A 15/30/15 is recommended. Miracle Gro is such a ratio.

Once your friend does get her geraniums to last until the fall, tell her she should plan on saving them....from year, to year, to year. Maybe, she need never buy another geranium.

It might be worthwhile to grow a few plants in pots alongside the plants in the ground and to compare the results. Pelargonium plants can be grown in 5"-6" pots in good general purpose potting compost plus a little sharp sand. Good drainage and good light are important. Plants should not be put out while there is a risk of frost and should be brought into frost free conditions before winter frosts.

Since it has already happened twice, it wouldn't hurt to replace a large amount of soil - 1 or more cubic ft at the planting site. She can use a regular potting mix or miracle gro. A container or hanging basket would also work equally well.

I grew several geraniums in red clay mound around a tree. ( I didn't know much about geraniums last yr.. I am newbie). I did use a handful of fertilizer. The builder had planted the tree and dumped clay around the tree. Many of those geraniums survived the winter after blooming profusely even though they shed the leaves in november and looked almost dead. I pulled them out while I was cleaning last week and found that they were actually alive, so I started to revive them in a separate container. I may have been lucky.

Here is a link that might be useful: Geranium problems

I would have to say it is either the site location, watering/fertilizer program, or.. has she purchased from the same nursery every year? I know the one year I picked up some white zonal geraniums for an accent planting. The plants were most definetly stunted with growth regulator on them. Side by side my seed grown and those, my seed grown out preformed the store purchased ones. I took em back for a refund.

I grow the same geraniums year after year. Your best bet is to grow them in a clay pot. They hold water in the soil a lot less than plastic pots do. The soil should be good quality potting soil with a lot of perlite added for drainage. What you want to end up with is a light, fluffy soil that will not get waterlogged. To save them over the winter, just bring them in before a frost, set them in the basement, no water until February and then only a very, very small drink. No water at all as long as they are trying to push out green shoots. In the spring, bring them up, put them outside, cut them back and watch them grow. If you bring them up early to get a head start, make sure you bring them in if a frost is predicted at night. For a brilliant red one, try "Forever Red".