Ven. Thanissaro's translation here (quoted below) reads:
"Now what, lady, lies on the other side of pleasant feeling?"
"Passion lies on the other side of pleasant feeling."
"And what lies on the other side of painful feeling?"
"Resistance lies on the other side of painful feeling."
If you read this footnote on Ven. Thanissaro's translation, it says:
This reading follows the Thai edition of the Pali canon. The PTS
edition of the Pali canon gives the first two questions and answers in
this exchange as follows:
"Now what, lady, lies on the other side of pleasant feeling?"
"Painful feeling lies on the other side of pleasant feeling."
"And what lies on the other side of painful feeling?"
"Pleasant feeling lies on the other side of painful feeling."
For some reason, the editors of neither edition seem to have been
aware of the reading in the other edition.
Now, SuttaCentral's translation here (quoted below) by Ven. Sujato:
“But ma’am, what is the counterpart of pleasant feeling?”
“Painful feeling.”
“What is the counterpart of painful feeling?”
“Pleasant feeling.”
So, that solves it. It's because the two Pali source editions are different.
However, I could not find the Pali text associated with Ven. Thanissaro's translation.
I can find something similar here in SN 36.6:
When they’re touched by painful feeling, they resist it. (Ven. Sujato here)
As he is touched by that painful feeling, he is resistant. (Ven. Thanissaro here)
Being contacted by that same painful feeling, he harbours aversion towards it. (Ven. Bodhi here)
When touched by that painful feeling, he is aversive. (Ven. Suddhaso here)
Tassāyeva kho pana dukkhāya vedanāya phuṭṭho samāno paṭighavā hoti.
According to the Concise Pali-English Dictionary by Ven. A.P. Buddhadatta Mahathera:
paṭigha: [m.] anger; repulsion; collision.
So, it can be resistance, repulsion, aversion, that one feels towards painful feelings.
Why counterparts or opposites?
From Piya Tan's commentary on MN 44:
2.8 OPPOSITES AND CONTRASTS (PAṬIBHĀGA) [§29]. The
closing question 28-34 deals with paṭibhāga,
that is, the 7 key aspects [§29] and their contrary or
contrasting qualities (except for
the last case, nirvana). The general idea here is to present an
overview of the relativity amongst feelings, knowledge and liberation,
and how this leads to nirvana. If something has an opposite (in real
or existential terms), it means that it is not absolute, and that its
nature or conception is meaningful only because its opposite, or
contrasting it with something else. But whatever can be contrasted in
this way must be relative. For example, ignorance is said to be the
opposite of neutral feeling because the latter is subtle and difficult
to detect. Each time we ignore a neutral feeling, we reinforce our
ignorance of it; we learn nothing of it. The remedy here is to review
― neutral-feeling experiences, especially after a meditation, or after
any significant event in our lives, or as a daily practice, that is,
to reflect on them as being impermanent.
Nirvana is unique. In intellectual or worldly terms,
it may be understood as ― sub specie aeternitatis,
that is, something eternal,
universal, nothing to do with time. By its very nature — as the
unconditioned (asaṅkhata) — it has no opposite or comparison. In a
manner of speaking, the way out of suffering is called ― nirvana,
but this is merely to inspire and move us with the fact and
possibility of the way out of suffering. Since nirvana is
unconditioned, it has neither an opposite nor a complement.