SS is taxed up to 85%

https://smartasset.com/retirement/is-social-security-income-taxable

Since her household income is more than $44,000, chances are her SS will be taxed at 85%.  Not 100% of her SS is taxable. 

Therefore your formula would be  (401K withdrawal + 85% of SS + other income) < $109450

Of course only the income above $109450 would be taxed at 22%, e.g. if income is $100,000, only $550 (100,000-109450) would be taxed at 22%.   So she's free to experiment on how much 401K withdraw she could make to optimize her number for the future years.