The US is where the pharma giant makes more than half its turnover and is "still the leading market in the world in terms of the launches of new drugs and vaccines," she says.
Alongside China, it is "the best market in the world to do business development".
GSK's latest stateside investment drive followed US pharmaceutical company Merck - which is called MSD in Europe – scrapping a planned £1bn expansion of its UK operations.
UK drug maker AstraZeneca has also announced it is pausing a planned £200m investment in a Cambridge research facility while ploughing tens of billions of dollars into the US.
Other drug companies have also said there is little appetite to invest in the UK, which successive governments have insisted is a life sciences superpower.