She drives her sisters to the Qur’aan school and she stipulated that they should teach her adhkaar and du‘aa’s in return for that

Firstly: 

There is no doubt that part
of a person’s understanding and eagerness for good is that his righteous
deeds should be sincerely for Allah and free of any other motives such as
making gains, whether it tangible or intangible, even if it is only thanks
from the person he treated kindly or a du‘aa’ that he asks for from the
person for whom he did a favour. 

Hence Allah, may He be
glorified and exalted, said concerning His believing slaves, the people of
the highest levels of Paradise (interpretation of the meaning):

“And
they give food, in spite of their love for it (or for the love of Him), to
Miskin (the poor), the orphan, and the captive,

(Saying): ‘We feed you seeking Allâh’s Countenance only. We
wish for no reward, nor thanks from you. ‘Verily, We fear from our Lord a
Day, hard and distressful, that will make the faces look horrible (from
extreme dislike to it)’”

[al-Insaan 76:8-10]. 

It was narrated from ‘Ubayd
Abu’l-Ja‘d that ‘Aa’ishah said: 

A sheep was given to the
Messenger of Allah (blessings and peace of Allah be upon him) and he said:
Divide it into portions and distribute it. Every time the servant came back,
‘Aa’ishah said: What did they say to you? She (the servant) said: What else
could they say? (They said): Baarak Allahu fikum (May Allah bless you).
‘Aa’ishah said: And may Allah bless them; we say to them the same as they
said to us, and the reward will still be saved for us. 

Narrated by al-Nasaa’i in
‘Aml al-Yawm wa’l-Layla, 303; also by Ibn al-Sunni, 277. Shaykh
al-Albaani (may Allah have mercy on him) said: Its isnaad is jayyid.
Takhreej al-Kalim al-Tayyib, no. 175 

Secondly: 

You and your sisters who go
with you should have hasten to include your sister in this  righteous act
that you are doing, even if you did not owe her a favour for driving you.
This is part of loving good for the Muslims and the duty of spreading good
among the people. 

If you did not do that and
she is eager for the good that you have, there is nothing wrong with her
stipulating this benefit in return for driving you, although it would have
been better in her case to do that sincerely for the sake of Allah alone
rather than asking you for something. She should strive to do righteous
deeds and attend the lessons with you as if she is one of you. That would
combine two good things, helping her sisters to do something good and
seeking reward for it with Allah, as well as attaining the same benefits as
you. 

If her circumstances do not
allow that and she needs help from you, then you should give her this help
and there is nothing wrong with her asking for it from you. 

And Allah knows best.