@Pembroke37 NCpeson is correct about the sale of the mineral rights. NORMALLY, there is a stepped-up basis as of the date of death (let's say $1,000). If the rights are subsequently sold then any profit or loss on the sale will be based on the stepped-up basis, not the basis prior to the date of death. NOTE that this is the case for securities (stocks, bonds, mutuals, real estate, etc.) but I am not well versed on mineral rights so you should not take this as anything but advice to find this out for yourself. Download IRS publications, 551 and 559 for a start.
You can also request a waiver of the penalty by checking box A in part II of form 2210. You will need to attach an explanation as to why you are requesting the waiver. It also wouldn't hurt to attach a copy of your mother's death certificate and document when you received the unexpected income. The IRS might be more sympathetic if it was very late in December.
