Assalm Alaikom,
Subject: Unable to fulfill a pledge.
A person applied for a job and pledged that if she gets the job, she will be fasting one month per year, other than Ramadan, and shall pray 20 additional Rakaa daily, for the rest of her life. She got the job. But she been unable to fulfill any of the above pledges as deemed very difficult. Question: How can she cancel the pledge permanently?

So long as this lady is unable to fulfill her vow, she must expiate for this by either feeding or providing garments for 10 poor people. This is based on the words of the Prophet (peace and blessings be upon him), "He who made a vow, without naming it, must expiate for it the same way he expedites for breaking an oath; he who made a vow and unable to fulfill, let him expiate for it the same he expiates for breaking an oath; and he who made a vow and is able to fulfill, let him do." [Recorded by IbnMaja]