First off, Valorum wasn't sending any help, he was only sending people to check if she was telling the truth.
VALORUM: Will you defer your motion
to allow a commission
to explore the validity
of your accusations?
Palpatine had convinced her that Vallorum was incapable of acting in a timely manner to help them, saying bureaucracy and corruption limited the ability to act effectively and swiftly.
PALPATINE: There is no civility,
is not what it once was.
The senate is full of greedy,
There is no interest
in the common good.
I must be frank, Your Majesty.
There is little chance the senate
will act on the invasion
AMIDALA: Chancellor Valorum
seems to think there is hope.
PALPATINE: If I may say so, Your Majesty...
has little real power.
He is mired by baseless
accusations of corruption.
- The bureaucrats are in charge now.
AMIDALA: What options have we?
PALPATINE: Our best choice would be
to push for the election...
of a stronger
one who could control
and give us justice.
You could call for a vote of
no confdence in Chancellor Valorum.
AMIDALA: He has been
our strongest supporter.
PALPATINE: Our only other choice would be
to submit a plea to the courts.
AMIDALA: The courts take even longer
to decide things than the senate.
Our people are dying, Senator.
We must do something quickly
to stop the Federation.
So, when she saw Valorum was only going to send people to check if there was a problem, rather than take real action to help Naboo, the Queen took this as proof Palpatine was right. She therefore felt a vote of no confidence, getting a new leader who could/would do something, was her only option left.
PALPATINE: now they will elect a new chancellor, a strong chancellor. One that will not let our tragedy to continue.
As it turns out, this all was part of his plan to
become chancellor and rule the galaxy.
All quotes from the film's script