There is no legal requirement that a person hires an attorney to prepare a will (or any other document) for the person. If the person meets of the statutory requirements for a valid will, then the will the person self-prepares will be as valid as any will prepared by a competent attorney.
The value of the services of a competent attorney lies in recognizing how the law likely will be applied to the particular facts of a client.
In this particular case, the husband may still have the right to force the sale of the house even if the son does becomes an owner.
Attorney's fees can sometimes be expensive. However, doing things right the first time is much less expensive than correcting mistakes.
To lessen the chances of doing things incorrectly, the friend likely should review her facts and options with an attorney.
Your friend also needs to keep in mind a spouse's "right of election" That is, a spouse can contest a will if it leaves the spouse with less than their rightful share. Also, the deed to the house may be written in such a way that it passes outside the estate with an automatic right of surviviorship. It might be easier to just add the son to a new deed if the father consents. If there is still a mortgage on the premises then the bank may have to be notified as well and the son added to the note and mortgage. I agree with the previous answer in that you should try to convince your friend it is worth the time and money to consult with a lawyer in your area.