Can income from a grant organization be considered compensation?

An individual works full-time as a private school administrator. She receives 20% of her income from her employer and the other 80% from a separate grant organization. Each pay period she receives two checks, one from her employer and the other from the grant organization.

Both sources of income are considered taxable income.

She is eligible to participate in the employer's 403(b).

QUESTION: Can then money from the grant organization be considered compensation for calculating her contributions as well as for purposes of determining includible compensation (415c limit)?

Is the grantor a § 501(c)(3) charitable organization?

Is the grantor a supporting organization of the school?

Is the grantor a part of the same § 414(c) employer as the school?

For example, the school and the grantor (if both are charities) might be one employer if there is enough overlap between their governing boards. Or, the school and the grantor might be one employer if they coordinate their activities and permissively aggregate.

26 C.F.R. § 1.414(c)-5 https://www.ecfr.gov/current/title-26/section-1.414(c)-5.

If the grantor is not a part of the same employer as the school, is the grantor nonetheless a participating employer under the school’s § 403(b) plan?

What are the plan’s governing documents’ provisions?

How is that 80% paid to her, via a W2 with taxes withheld or a 1099 as a contractor?

Since grant is paid directly to the administrator, it might be self-employment income to her in which case she may be able to do her own retirement plan on that income.

Who "owns" the grant, the individual or the school? If she leaves does the grant go with her or does it pay her replacement? It seems like she owns the grant, otherwise why wouldn't it be paid to the school which then uses to fund that 80% portion of her salary?

Need to know which rabbit hole we're going down first before we can get to a useful answer - and not just my questions or Peter's, all of them.

5 hours ago, CuseFan said:

How is that 80% paid to her, via a W2 with taxes withheld or a 1099 as a contractor?

KaJay, I think both Peter and CuseFan are right on with their comments, but I would start with the above and whose name and EIN are on the W-2, if it is  W-2.